Thermal Regulation For Wireless Charging Pad

ABSTRACT

A wireless charging device has a controller and at least one coil that is positioned near the surface of the charging device and configured to transmit an electromagnetic field and a first driver circuit configured to drive the transmitting coil. The controller is configured to cause the driver circuit to provide a charging current to the transmitting coil, decode a request for lower transmission power from a modulation of the charging current, reduce the amplitude of the charging current in accordance with the request for lower transmission power when a temperature measured at a surface of the charging device is less than a threshold temperature, and initiate a cool down sequence when the temperature measured at the surface of the charging device equals or exceeds the threshold temperature. In one example, the request for lower transmission power may be provided in an ASK-modulated signal superimposed on the charging current.

TECHNICAL FIELD

The present invention relates generally to wireless charging ofbatteries, including batteries in mobile computing devices, and moreparticularly to detection and amelioration of overheating duringcharging.

BACKGROUND

Wireless charging systems have been deployed to enable certain types ofdevices to charge internal batteries without the use of a physicalcharging connection. Devices that can take advantage of wirelesscharging include mobile processing and/or communication devices.Standards, such as the Qi standard defined by the Wireless PowerConsortium enable devices manufactured by a first supplier to bewirelessly charged using a charger manufactured by a second supplier.Standards for wireless charging are optimized for relatively simpleconfigurations of devices and tend to provide basic chargingcapabilities.

Improvements in wireless charging capabilities are required to supportcontinually increasing complexity of mobile devices and changing formfactors. For example, there is a need for a faster, lower powerdetection techniques that enable a charging device to detect and locatechargeable devices on a surface of a charging device, and to detectremoval or relocation of a chargeable device during a wireless chargingoperation.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates an example of a charging cell that may be provided ona charging surface provided by a wireless charging device in accordancewith certain aspects disclosed herein.

FIG. 2 illustrates an example of an arrangement of charging cellsprovided on a single layer of a segment of a charging surface providedby a wireless charging device in accordance with certain aspectsdisclosed herein.

FIG. 3 illustrates an example of an arrangement of charging cells whenmultiple layers of charging cells are overlaid within a segment of acharging surface provided by a wireless charging device in accordancewith certain aspects disclosed herein.

FIG. 4 illustrates the arrangement of power transfer areas provided by acharging surface of a charging device that employs multiple layers ofcharging cells configured in accordance with certain aspects disclosedherein.

FIG. 5 illustrates a wireless transmitter that may be provided in acharger base station in accordance with certain aspects disclosedherein.

FIG. 6 illustrates a microcontroller that supports ASK demodulation inaccordance with certain aspects disclosed herein.

FIG. 7 illustrates examples of encoding schemes that may be adapted todigitally encode messages exchanged between power receivers and powertransmitters in accordance with certain aspects disclosed herein.

FIG. 8 illustrates a topology that supports direct drive of transmittingcoils in a wireless charger adapted in accordance with certain aspectsdisclosed herein.

FIG. 9 provides a two-dimensional view showing temperature sensorsprovided on a surface of a wireless charging device in accordance withcertain aspects of this disclosure.

FIG. 10 provides cross-sectional views showing configurations oftemperature sensors provided in accordance with certain aspects of thisdisclosure.

FIG. 11 illustrates a cooling process managed by a wireless chargingdevice in accordance with certain aspects of this disclosure.

FIG. 12 illustrates a first example of a method for managing thermalcooling in a device being charged by a multi-coil wireless chargingsystem in accordance with certain aspects of this disclosure.

FIG. 13 illustrates one example of an apparatus employing a processingcircuit that may be adapted according to certain aspects disclosedherein.

FIG. 14 illustrates a second example of a method for managing thermalcooling in a device being charged by a multi-coil wireless chargingsystem in accordance with certain aspects of this disclosure.

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appendeddrawings is intended as a description of various configurations and isnot intended to represent the only configurations in which the conceptsdescribed herein may be practiced. The detailed description includesspecific details for the purpose of providing a thorough understandingof various concepts. However, it will be apparent to those skilled inthe art that these concepts may be practiced without these specificdetails. In some instances, well known structures and components areshown in block diagram form in order to avoid obscuring such concepts.

Several aspects of wireless charging systems will now be presented withreference to various apparatus and methods. These apparatus and methodswill be described in the following detailed description and illustratedin the accompanying drawing by various blocks, modules, components,circuits, steps, processes, algorithms, etc. (collectively referred toas “elements”). These elements may be implemented using electronichardware, computer software, or any combination thereof. Whether suchelements are implemented as hardware or software depends upon theparticular application and design constraints imposed on the overallsystem.

By way of example, an element, or any portion of an element, or anycombination of elements may be implemented with a “processing system”that includes one or more processors. Examples of processors includemicroprocessors, microcontrollers, digital signal processors (DSPs),field programmable gate arrays (FPGAs), programmable logic devices(PLDs), state machines, gated logic, discrete hardware circuits, andother suitable hardware configured to perform the various functionalitydescribed throughout this disclosure. One or more processors in theprocessing system may execute software. Software shall be construedbroadly to mean instructions, instruction sets, code, code segments,program code, programs, subprograms, software modules, applications,software applications, software packages, routines, subroutines,objects, executables, threads of execution, procedures, functions, etc.,whether referred to as software, firmware, middleware, microcode,hardware description language, or otherwise. The software may reside ona processor-readable storage medium. A processor-readable storagemedium, which may also be referred to herein as a computer-readablemedium may include, by way of example, a magnetic storage device (e.g.,hard disk, floppy disk, magnetic strip), an optical disk (e.g., compactdisk (CD), digital versatile disk (DVD)), a smart card, a flash memorydevice (e.g., card, stick, key drive), Near Field Communications (NFC)token, random access memory (RAM), read only memory (ROM), programmableROM (PROM), erasable PROM (EPROM), electrically erasable PROM (EEPROM),a register, a removable disk, a carrier wave, a transmission line, andany other suitable medium for storing or transmitting software. Thecomputer-readable medium may be resident in the processing system,external to the processing system, or distributed across multipleentities including the processing system. Computer-readable medium maybe embodied in a computer-program product. By way of example, acomputer-program product may include a computer-readable medium inpackaging materials. Those skilled in the art will recognize how best toimplement the described functionality presented throughout thisdisclosure depending on the particular application and the overalldesign constraints imposed on the overall system.

Overview

Certain aspects of the present disclosure relate to systems, apparatusand methods applicable to wireless charging devices and techniques.Charging cells may be configured with one or more inductive coils toprovide a charging surface in a charging device where the chargingsurface enables the charging device to charge multiple chargeabledevices wirelessly. The location of a device to be charged may bedetected through sensing techniques that associate location of thedevice to changes in a physical characteristic centered at a knownlocation on the charging surface. Sensing of location may be implementedusing capacitive, resistive, inductive, touch, pressure, load, strain,and/or another appropriate type of sensing.

In one aspect of the disclosure, an apparatus has a battery chargingpower source, a plurality of charging cells configured in a matrix, afirst plurality of switches in which each switch is configured to couplea row of coils in the matrix to a first terminal of the battery chargingpower source, and a second plurality of switches in which each switch isconfigured to couple a column of coils in the matrix to a secondterminal of the battery charging power source. Each charging cell in theplurality of charging cells may include one or more coils surrounding apower transfer area. The plurality of charging cells may be arrangedadjacent to the charging surface of the charging device without overlapof power transfer areas of the charging cells in the plurality ofcharging cells.

In some instances, the apparatus may also be referred to as a chargingsurface. Power can be wirelessly transferred to a receiving devicelocated anywhere on a surface of the apparatus. The devices can have anarbitrarily defined size and/or shape and may be placed without regardto any discrete placement locations enabled for charging. Multipledevices can be simultaneously charged on a single charging surface. Theapparatus can track motion of one or more devices across the chargingsurface. Certain concepts disclosed herein apply equally to a chargingdevice that has a single transmitting coil or charging cell.

In various aspects of the disclosure, a wireless charging deviceconfigured for multi-device charging may determine, calculate orestimate when an over-temperature condition exists in one of multipledevices being concurrently charged. The wireless charging device maytake steps to reduce the temperature in a receiving device identified ashaving an overtemperature condition. The wireless charging device mayconfigure a driver circuit to drive a transmitting coil positioned nearthe surface of the charging device, cause the driver circuit to providea charging current to the transmitting coil, and decode a request forlower transmission power from a modulation of the charging current,determine whether an overtemperature condition exists or is indicated ina device being charged. The overtemperature condition may correspond toa temperature of a battery exceeding a maximum temperature defined bystandards, protocol or designer. The overtemperature condition may beindicated when a temperature measured at the surface of the chargingdevice exceeds a threshold temperature. The wireless charging device mayreduce the amplitude of the charging current in accordance with therequest for lower transmission power when a temperature measured at asurface of the charging device is less than the threshold temperature.The wireless charging device may initiate a cool down sequence when thetemperature measured at the surface of the charging device equals orexceeds the threshold temperature.

Charging Cells

According to certain aspects disclosed herein, a charging surface may beprovided using charging cells in a charging device, where the chargingcells are deployed adjacent to the charging surface. In one example thecharging cells are deployed in one or more layers of the chargingsurface in accordance with a honeycomb packaging configuration. Acharging cell may be implemented using one or more coils that can eachinduce a magnetic field along an axis that is substantially orthogonalto the charging surface adjacent to the coil. In this description, acharging cell may refer to an element having one or more coils whereeach coil is configured to produce an electromagnetic field that isadditive with respect to the fields produced by other coils in thecharging cell and directed along or proximate to a common axis.

In some implementations, a charging cell includes coils that are stackedalong a common axis and/or that overlap such that they contribute to aninduced magnetic field substantially orthogonal to the charging surface.In some implementations, a charging cell includes coils that arearranged within a defined portion of the charging surface and thatcontribute to an induced magnetic field within the substantiallyorthogonal portion of the charging surface associated with the chargingcell. In some implementations, charging cells may be configurable byproviding an activating current to coils that are included in adynamically defined charging cell. For example, a charging device mayinclude multiple stacks of coils deployed across the charging surface,and the charging device may detect the location of a device to becharged and may select some combination of stacks of coils to provide acharging cell adjacent to the device to be charged. In some instances, acharging cell may include, or be characterized as a single coil.However, it should be appreciated that a charging cell may includemultiple stacked coils and/or multiple adjacent coils or stacks ofcoils. The coils may be referred to herein as charging coils, wirelesscharging coils, transmitter coils, transmitting coils, powertransmitting coils, power transmitter coils, or the like.

FIG. 1 illustrates an example of a charging cell 100 that may bedeployed and/or configured to provide a charging surface of a chargingdevice. As described herein, the charging surface may include an arrayof charging cells 100 provided on one or more substrates 106. A circuitcomprising one or more integrated circuits (ICs) and/or discreteelectronic components may be provided on one or more of the substrates106. The circuit may include drivers and switches used to controlcurrents provided to coils used to transmit power to a receiving device.The circuit may be configured as a processing circuit that includes oneor more processors and/or one or more controllers that can be configuredto perform certain functions disclosed herein. In some instances, someor all of the processing circuit may be provided external to thecharging device. In some instances, a power supply may be coupled to thecharging device.

The charging cell 100 may be provided in close proximity to an outersurface area of the charging device, upon which one or more devices canbe placed for charging. The charging device may include multipleinstances of the charging cell 100. In one example, the charging cell100 has a substantially hexagonal shape that encloses one or more coils102, which may be constructed using conductors, wires or circuit boardtraces that can receive a current sufficient to produce anelectromagnetic field in a power transfer area 104. In variousimplementations, some coils 102 may have a shape that is substantiallypolygonal, including the hexagonal charging cell 100 illustrated inFIG. 1. Other implementations provide coils 102 that have other shapes.The shape of the coils 102 may be determined at least in part by thecapabilities or limitations of fabrication technology, and/or tooptimize layout of the charging cells on a substrate 106 such as aprinted circuit board substrate. Each coil 102 may be implemented usingwires, printed circuit board traces and/or other connectors in a spiralconfiguration. Each charging cell 100 may span two or more layersseparated by an insulator or substrate 106 such that coils 102 indifferent layers are centered around a common axis 108.

FIG. 2 illustrates an example of an arrangement 200 of charging cells202 provided on a single layer of a segment of a charging surface of acharging device that may be adapted in accordance with certain aspectsdisclosed herein. The charging cells 202 are arranged according to ahoneycomb packaging configuration. In this example, the charging cells202 are arranged end-to-end without overlap. This arrangement can beprovided without through-hole or wire interconnects. Other arrangementsare possible, including arrangements in which some portion of thecharging cells 202 overlap. For example, wires of two or more coils maybe interleaved to some extent.

FIG. 3 illustrates an example of an arrangement of charging cells fromtwo perspectives 300, 310 when multiple layers are overlaid within asegment of a charging surface that may be adapted in accordance withcertain aspects disclosed herein. Layers of charging cells 302, 304,306, 308 are provided within a segment of a charging surface. Thecharging cells within each layer of charging cells 302, 304, 306, 308are arranged according to a honeycomb packaging configuration. In oneexample, the layers of charging cells 302, 304, 306, 308 may be formedon a printed circuit board that has four or more layers. The arrangementof charging cells 100 can be selected to provide complete coverage of adesignated charging area that is adjacent to the illustrated segment.

FIG. 4 illustrates the arrangement of power transfer areas provided in acharging surface 400 that employs multiple layers of charging cellsconfigured in accordance with certain aspects disclosed herein. Theillustrated charging surface is constructed from four layers of chargingcells 402, 404, 406, 408. In FIG. 4, each power transfer area providedby a charging cell in the first layer of charging cells 402 is marked“L1”, each power transfer area provided by a charging cell in the secondlayer of charging cells 404 is marked “L2”, each power transfer areaprovided by a charging cell in the third layer of charging cells 406 ismarked “L3”, and each power transfer area provided by a charging cell inthe fourth layer of charging cells 408 is marked “L4”.

Wireless Transmitter

FIG. 5 illustrates a wireless transmitter 500 that may be provided in acharger base station. A controller 502 may receive a feedback signalfiltered or otherwise processed by a conditioning circuit 508. Thecontroller may control the operation of a driver circuit 504 thatprovides an alternating current to a resonant circuit 506 that includesa capacitor 512 and inductor 514. The resonant circuit 506 may also bereferred to herein as a tank circuit, LC tank circuit, or LC tank, andthe voltage 516 measured at an LC node 510 of the resonant circuit 506may be referred to as the tank voltage.

The wireless transmitter 500 may be used by a charging device todetermine if a compatible device has been placed on a charging surfaceduring a discovery procedure. For example, the charging device maydetermine that a compatible device has been placed on the chargingsurface by sending an intermittent test signal (active ping) through thewireless transmitter 500, where the resonant circuit 506 may detect orreceive encoded signals when a compatible device responds to the testsignal. The charging device may be configured to activate one or morecoils in at least one charging cell after receiving a response signaldefined by standard, convention, manufacturer or application. In someexamples, the compatible device can respond to a ping by communicatingreceived signal strength such that the charging device can find anoptimal charging cell to be used for charging the compatible device. Thediscovery procedure may enable the charging device to determine acharging configuration to be used for charging the discovered device.The charging configuration may define one or more transmitting coils orcharging cells that will receive a charging current when charging adiscovered device, a level of the power to be transmitted to thediscovered device, maximum and minimum levels of power to be transmittedto the discovered device.

Passive ping techniques may use the voltage and/or current measured orobserved at the LC node 510 to identify the presence of a receiving coilin proximity to the charging pad of a device adapted in accordance withcertain aspects disclosed herein. In many conventional wireless chargertransmitters, circuits are provided to measure voltage at the LC node510 or to measure the current in the LC network. These voltages andcurrents may be monitored for power regulation purposes or to supportcommunication between devices. In the example illustrated in FIG. 5,voltage at the LC node 510 is monitored, although it is contemplatedthat current may additionally or alternatively be monitored to supportpassive ping in which a short pulse is provided to the resonant circuit506. A response of the resonant circuit 506 to a passive ping (initialvoltage Vo) may be represented by the voltage (V_(LC)) at the LC node510, such that:

$\begin{matrix}{V_{LC} = {V_{0}{e^{{- {(\frac{\omega}{2Q})}}t}.}}} & \left( {{Eq}.\mspace{14mu} 1} \right)\end{matrix}$

According to certain aspects disclosed herein, coils in one or morecharging cells may be selectively activated to provide an optimalelectromagnetic field for charging a compatible device. In someinstances, coils may be assigned to charging cells, and some chargingcells may overlap other charging cells. In the latter instances, anoptimal charging configuration may be selected at the charging celllevel. In other instances, charging cells may be defined based onplacement of a device to be charged on a surface of the charging device.In these other instances, the combination of coils activated for eachcharging event can vary. In some implementations, a charging device mayinclude a driver circuit that can select one or more cells and/or one ormore predefined charging cells for activation during a charging event.

The charging device may define a charging configuration based in part oninformation received from the device to be charged. The device to becharged may communicate its identity and requested power transfer levelby modulating current received through power transfer from the chargingdevice. The device to be charged may modulate the received current bychanging the load it presents to a receiving coil. Changes in load arereflected through the electromagnetic coupling to the charging devicewhich may capture modulation signals by measuring tank voltage orcurrent flowing through a transmitting coil. In one example, informationmay be encoded in the tank voltage using Amplitude Shift Key (ASK)modulation.

FIG. 6 illustrates an example of a processing circuit 600 that may beconfigured to receive and decode ASK-modulated signal. The processingcircuit 600 includes a processor 602, which may be coupled to a memorydevice 604 and/or registers that can store messages to be transmittedusing an ASK-modulated signal 612 and/or messages decoded from areceived ASK-modulated signal 612. The processing circuit 600 includesan ASK decoder 606 that may be implemented using hardware, software orsome combination of hardware and software. The ASK decoder 606 may use aclock signal received from a clock generation or recovery circuit tocontrol timing of the transmitted ASK-modulated signal 612 and tocontrol sampling and decoding of a received ASK-modulated signal 612.

FIG. 7 illustrates examples of encoding schemes 700, 720 that may beadapted to digitally encode messages exchanged between power receiversand power transmitters. In the first example, a differential bi-phaseencoding scheme 700 encodes binary bits in the phase of a data signal704. In the illustrated example, each bit of a data byte 706 is encodedin a corresponding cycle 708 of an encoder clock signal 702. The valueof each bit is encoded in the presence or absence of a transition 710(phase change) in the data signal 704 during the corresponding cycle708.

In the second example, a power supply 724 is encoded using a powersignal amplitude encoding scheme 720. In the illustrated example, binarybits of a data byte 726 are encoded in level of the power supply 724.Each bit of the data byte 726 is encoded in a corresponding cycle 728 ofan encoder clock signal 722. The value of each bit is encoded in thevoltage level of the power supply 724 relative to a nominal 100% voltagelevel 730 of the power supply 724 during the corresponding cycle 708.

Selectively Activating Coils

According to certain aspects disclosed herein, transmitting coils in oneor more charging cells may be selectively activated to provide anoptimal electromagnetic field for charging a compatible device. In someinstances, transmitting coils may be assigned to charging cells, andsome charging cells may overlap other charging cells. In the latterinstances, the optimal charging configuration may be selected at thecharging cell level. In other instances, charging cells may be definedbased on placement of a device to be charged on a surface of thecharging device. In these other instances, the combination of coilsactivated for each charging event can vary. In some implementations, acharging device may include a driver circuit that can select one or morecells and/or one or more predefined charging cells for activation duringa charging event.

FIG. 8 illustrates an example of a topology 800 in which each coil orcharging cell is individually and/or directly driven by a driver circuit802 in accordance with certain aspects disclosed herein. The drivercircuit 802 may be configured to select one or more coils or chargingcells 100 from a group of coils 804 to charge a receiving device. Itwill be appreciated that the concepts disclosed here in relation tocharging cells 100 may be applied to selective activation of individualcoils or stacks of coils. Charging cells 100 that are not in use receiveno current flow. A relatively large number of charging cells 100 may bein use and a switching matrix may be employed to drive individual coilsor groups of coils. In one example, a first switching matrix mayconfigure connections that define a charging cell or a group of coils tobe used during a charging event and a second switching matrix may beused to activate the charging cell and/or a group of selected coils.

In some implementations, a matrix switching scheme may be employed toselect the charging cells 100 from the group of coils 804 to charge areceiving device. A relatively large number of charging cells 100 may beused in the honeycomb packaging configuration illustrated in FIGS. 2 and3, and at least some of the charging cells 100 may be logically arrangedor connected in a switching matrix. The use of a switching matrix cansignificantly reduce the number of switching components needed tooperate a network of tuned LC circuits. For example, N individuallyconnected cells require at least N switches, whereas a two-dimensionalmatrix having N cells can be operated with √N switches. In one example,a 9-cell implementation can be implemented in a 3×3 matrix using 6switches, saving 3 switches. In another example, a 16-cellimplementation can be implemented in a 4×4 matrix using 8 switches,saving 8 switches. During operation at least 2 switches are closed toactively couple one coil to a wireless transmitter and/or receivercircuit. Multiple switches can be closed at once in order to facilitateconnection of multiple coils to the wireless transmitter and/or receivercircuit. Multiple switches may be closed, for example, to enable modesof operation that drive multiple transmitting coils when transferringpower to a receiving device.

Thermal Regulation in a Multi-Device, Multi-Coil Wireless Charger

Batteries used in mobile communication devices may be susceptible toheating issues under high current draw or current high current chargingoperations. A battery installed in a device may be susceptible tooverheating when the device has limited heatsinking or heat dissipationcapabilities. For example, a battery in a mobile communication devicemay be located within a small space that closely matches the volume ofthe battery such that airflow is restricted. Restricted airflow caninhibit the dissipation of heat generated through losses incurred duringbattery charging and discharging, resulting in heat buildup near thebattery and within the mobile communication device as a whole. Controlof heat generation, buildup and dissipation is needed to prevent damageto batteries and to avoid potential runaway chemical reactions that canresult in detonation or combustion of constituents of the battery.Certain industry bodies define and promulgate standards and protocolsfor managing battery operation in a manner that protects batteries fromoverheating. For example, the Japan Electronics and InformationTechnology Industries Association (JEITA) defines operating limits forLithium-Ion batteries. Lithium-Ion batteries are widely used in portableelectronic equipment due in part to their high-energy density, and JEITAguidelines and procedures are intended to prevent ignition of LithiumIon batteries.

JEITA defines operating conditions that affect Lithium-Ion batteriesoperated at elevated temperatures. In one example, a pulsed currentcharging technique is used to improve the lifetime, charging speed,charge capacity, discharging capability and temperature control ofLithium-Ion batteries. JEITA defines a duty cycle that can range between20% and 80%.

Certain aspects of this disclosure provide techniques, circuits andmethods for monitoring, limiting and/or controlling overtemperatureevents in chargeable devices during battery charging, including when thecharging device is a multi-device, multi-coil wireless charger.Limitation and amelioration of overtemperature events throughmodifications to the charging configuration defined for or by thewireless charger can avoid the imposition of inefficient charging dutycycles when operating a chargeable device in accordance with JEITAprotocols.

The wireless charger is typically unaware of the temperature or state ofcharge of a battery in a device being charged. The device being chargedmay monitor battery temperature and may respond to temperature issues byrequesting lower charging power or by terminating charging until coolinghas been accomplished. Requests for lower charging power or terminationof charging by the device being charged can be made for various reasonsother than temperature-related reasons. For example, reductions incharging power may be requested when the battery in the device beingcharged is at full capacity or approaching full capacity. Accordingly,requests for changes in charging power are unreliable indicators fordistinguishing between requests based on battery charge and temperaturestate when the charging device is unaware of state of charge of abattery in a device being charged.

In one aspect of this disclosure, temperature measured at the surface ofa charging device (which may also be referred to as a “charging pad”)may be used to determine the likely reason for requests for changes incharging power. In one example, a request for a reduction in chargingpower when the temperature at the surface of the charging device isnominal or within a preconfigured range may indicate that the battery inthe device being charged is at full capacity or approaching fullcapacity. In another example, a request for a reduction in chargingpower when the temperature at the surface of the charging device exceedsnominal maximum temperature or falls outside a preconfigured range oftemperatures may indicate that the battery in the device being chargedis experiencing elevated temperatures.

FIGS. 9 and 10 illustrate configurations 900, 1000, 1020 of multidevicewireless charging devices that may be instrumented to measuretemperature in accordance with certain aspects of this disclosure. FIG.9 provides a two-dimensional view of a configuration 900 of the wirelesscharging device in which temperature sensors 904 ₁-904 ₆ and 906 ₁-906 ₄are deployed around the perimeter of an array of charging cells(LP1-LP18) provided on the surface 902 of the wireless charging device.A combination of horizontal temperature sensors 904 ₁-904 ₆ and verticaltemperature sensors 906 ₁-906 ₄ may enable an estimated or calculatedmapping of temperatures across the surface 902 of the wireless chargingdevice. The temperature sensors 904 ₁-904 ₆ and 906 ₁-906 ₄ may includethermocouples or other thermometric devices.

In other examples, temperature sensors may be provided at the center ofeach charging cell, or between each pair of charging cells. FIG. 10provides cross-sectional views of different configurations 1000, 1020 oftemperature sensors 1008 ₁-1008 ₃ and 1028 ₁-1028 ₃ provided in verticalalignment with corresponding charging cells 1004 ₁-1004 ₃. Thetemperature sensors 1008 ₁-1008 ₃ and 1028 ₁-1028 ₃ may includethermocouples or other thermometric devices. The temperature sensors1008 ₁-1008 ₃, 1028 ₁-1028 ₃ may be embedded in, attached to, orotherwise provided in thermal communication with a thermally conductivelayer 1006, 1026 located on or near the surface 902 of the wirelesscharging device.

The thermally conductive layer 1006, 1026 may further serve aselectrical insulation or may provide, enhance or configureelectromagnetic properties of the surface 902 of the wireless chargingdevice. In the first configuration 1000, the thermally conductive layer1006 is provided at or near the top of the surface 902 of the wirelesscharging device and below the charging cells 1004 ₁-1004 ₃. In thesecond configuration 1020, the thermally conductive layer 1026 isprovided in a layer above the charging cells 1004 ₁-1004 ₃. In otherconfigurations (not shown), temperature sensors may be provided in thesame layer as the charging cells and located at the center of eachcharging cell or between charging cells. A wireless charging device maybe configured to consider surface temperatures when determining whetherrequests for reduced power transfer indicate that a battery temperatureissue has been detected by the device being charged.

In some implementations, the temperature sensors 904 ₁-904 ₆, 906 ₁-906₄, 1008 ₁-1008 ₃ and 1028 ₁-1028 ₃ may be calibrated using instrumentedchargeable devices. In one example, an instrumented chargeable device isplaced on the surface 902 of the wireless charging device over one ormore charging cells 1004 ₁-1004 ₃. Internal temperature measurementstaken by the instrumented chargeable device and concurrent measurementsof surface temperature captured by the temperature sensors 904 ₁-904 ₆,906 ₁-906 ₄ or 1008 ₁-1008 ₃ may be compared and correlated to provideinformation usable by a controller 1002 in the wireless charging devicefor estimating internal temperatures of chargeable devices during normaloperation. In one example, the wireless charging device may beconfigured with a lookup table that can be indexed using surfacetemperatures of the wireless charging device to obtain estimates ofinternal temperatures of a device being charged during normal operation.

According to certain aspects of this disclosure, a wireless chargingdevice may determine that a device being charged is attempting to cooldown based on a combination of information that includes pad or surfacetemperature and requests for power draw. The wireless charging devicemay assist cooling by reducing charging power to a lowest level, whilemonitoring changes in temperature measured at the surface of thewireless charging device in order to estimate or infer that changes intemperature have occurred within the device being charged. The wirelesscharging device may terminate charging when temperature fails to declineat a sufficient rate. The wireless charging device may reduce orterminate charging for one or more other devices when temperature failsto decline at a sufficient rate after terminating charging for thedevice being cooled.

The graph 1100 in FIG. 11 illustrates a cooling process managed by awireless charging device in accordance with certain aspects of thisdisclosure. The graph includes a curve that represents a batterytemperature 1102 measured or estimated by the device being charged,which may have some correspondence or correlation to temperaturemeasured at the surface of the wireless charging device. The wirelesscharging device may estimate internal temperature of a device beingcharged based on temperatures measured at the surface of the wirelesscharging device.

Initially, battery temperature 1102 is increasing until a hightemperature limit 1130 is reached at a first point in time 1104. Thehigh temperature limit 1130 may correspond to a maximum temperaturedefined for the battery of the device being charged. Protocols orindustry standards may impose restrictions on charging power when themaximum temperature is reached. The device being charged may issuerequests to modify transmitted power that result in lower power transferrates. In one example, the device being charged may issue requests thatare intended to cause power transfer to conform to a duty cycle definedby protocols or standards for charging high-temperature batteries. Thelimitations imposed on charging through duty cycles may result ininefficiencies in charging and temperature reduction.

In one aspect, the wireless charging device may associate requests tomodify transmitted power with an overtemperature event when temperaturesmeasured at the surface of the wireless charging device exceed athreshold temperature level that indicates that the battery temperature1102 of the device being charged has reached the high temperature limit1130 or is within range of the high temperature limit 1130. The wirelesscharging device may enter a cooling mode 1120 when an overtemperatureevent is determined to have occurred. The cooling mode 1120 may persistuntil the measured or estimated battery temperature 1102 has reached alow temperature threshold 1132. Multiple phases or stages may be definedfor the cooling mode 1120.

A first stage 1122 of the cooling mode 1120 commences after the thermallimit is triggered or after the high temperature limit 1130 is reached.In the first stage 1122, the wireless charging device may reducetransmitted power to the lowest level that does not trigger or causedisconnection from the device being charged. The lowest level oftransmitted power may be associated with the lowest level of dissipatedpower for the device being charged and a drop in measured or estimatedbattery temperature 1102 may be expected. A limited duration may bedefined for the cooling mode 1120, and the battery temperature 1102 maybe expected to drop to the level of the low temperature threshold 1132within the duration of the cooling mode 1120. The thermal gradient ofthe battery temperature 1102 may be monitored to determine whetherbattery temperature 1102 is likely to fall below the low temperaturethreshold 1132 during the cooling mode 1120. In the illustrated example,the rate of change of the battery temperature 1102 varies and may becharacterized by multiple temperature gradients 1106, 1108, 1110.Temperature gradients 1106, 1108, 1110 may be calculated based on adifference in measured or estimated battery temperature 1102 over aperiod of time defined by a specified timer interval.

An initial temperature gradient 1106 is consistent with a likelihoodthat the battery temperature 1102 will reach the low temperaturethreshold 1132 while the cooling mode 1120 is in effect. The rate ofchange of the battery temperature 1102 decreases, as indicated by thetwo later occurring temperature gradients 1108 and 1110 and a levellingto a zero gradient 1112. Accordingly, in the illustrated example, it isapparent that the measured or estimated battery temperature 1102 willnot reach the low temperature threshold 1132 while the cooling mode 1120is in effect. In this example, the first stage 1122 is terminated and asecond stage 1124 is initiated.

In the second stage 1124, the wireless charging device terminates powertransmission to the device being charged. The absence of transmittedpower eliminates energy dissipation arising from charging and a drop1114 in battery temperature 1102 is expected in the absence of othersources of heating. The thermal gradient of the battery temperature 1102may be monitored to determine whether battery temperature 1102 is likelyto fall below the low temperature threshold 1132 during the cooling mode1120 within a preconfigured maximum cool down duration. Thepreconfigured maximum cool down duration may be defined by standards,protocol or based on information identifying the type or capabilities ofthe device being charged. The preconfigured maximum cool down durationmay be specified by the charging configuration defined for the devicebeing charged. In the illustrated example, the rate of change of thebattery temperature 1102 remains constant or has a gradient thatindicates that the battery temperature 1102 is unlikely to drop belowthe low temperature threshold 1132. Here the second stage 1124 isterminated and a third stage 1126 is initiated.

In the third stage 1124, power levels transmitted by the wirelesscharging device to one or more adjacent devices are reduced orterminated. In the third stage 1126, cooling is enforced across multipledevices and temperatures measured at charging cells involved in thecharging of the adjacent devices may also be monitored. In someimplementations, a thermal cutoff or limit can be applied globallyacross the surface 902 of the wireless charging device to cause alldevices to be cooled, thereby cooling the charging system including thewireless charging device and all devices placed on the surface 902 ofthe wireless charging device. The thermal gradient of the batterytemperature 1102 may be monitored to determine whether the batterytemperature 1102 is likely to fall below the low temperature threshold1132 during the cooling mode 1120. In the illustrated example, a drop1116 in the battery temperature 1102 occurs.

FIG. 12 is a flowchart 1200 that illustrates a first example of a methodfor managing thermal cooling in a device being charged by a multi-coilwireless charging system. The method be performed by a controller 1002in the multi-coil wireless charging system. The multi-coil wirelesscharging system may be capable of charging multiple chargeable devicesconcurrently. At block 1202, the controller 1002 may detect the presenceof a receiving device that has been placed on or near the surface 902 ofthe multi-coil wireless charging system. The controller 1002 mayinterrogate and/or negotiate with the receiving device to generate acharging configuration. The controller 1002 may then cause a chargingcurrent to be provided to one or more transmitting coils of themulti-coil wireless charging system in accordance with the chargingconfiguration.

At block 1204, the controller 1002 may determine whether a temperaturelimit has been reached in the receiving device. The temperature limitmay be related to the temperature of a battery being charged in thereceiving device. The temperature limit may be determined to have beenreached based on a temperature measured at the surface of the multi-coilwireless charging system. When the controller 1002 determines that thetemperature limit has not been reached, the charging continues at block1202. When the controller 1002 determines that the temperature limit hasbeen reached, the controller 1002 may interpret requests for powerreductions from the receiving device as an indication that the receivingdevice is attempting to reduce its temperature, and the controller 1002may proceed to block 1206.

In one example, the controller 1002 may determine at block 1206 whetherthe requested power level is below a minimum power level defined by thecharging configuration, protocol or system configuration. When therequested power level exceeds or equals the minimum power level,charging may continue at block 1202 at the requested, reduced powerlevel. When the requested power level is less than the minimum powerlevel, the controller 1002 may determine that the receiving device isattempting to cool down and may enter a cooling mode at block 1208. Thereceiving device may have requested less than minimum power level toimplement a duty cycle defined by protocols.

In some instances, the controller 1002 may respond to requests forchanges in transmitted power when the temperature limit has not beenreached. and one or more requests related to charging power levelsreceived from the receiving device.

Example of a Processing Circuit

FIG. 13 illustrates an example of a hardware implementation for anapparatus 1300 that may be incorporated in a charging device or in areceiving device that enables a battery to be wirelessly charged. Insome examples, the apparatus 1300 may perform one or more functionsdisclosed herein. In accordance with various aspects of the disclosure,an element, or any portion of an element, or any combination of elementsas disclosed herein may be implemented using a processing circuit 1302.The processing circuit 1302 may include one or more processors 1304 thatare controlled by some combination of hardware and software modules.Examples of processors 1304 include microprocessors, microcontrollers,digital signal processors (DSPs), SoCs, ASICs, field programmable gatearrays (FPGAs), programmable logic devices (PLDs), state machines,sequencers, gated logic, discrete hardware circuits, and other suitablehardware configured to perform the various functionality describedthroughout this disclosure. The one or more processors 1304 may includespecialized processors that perform specific functions, and that may beconfigured, augmented or controlled by one of the software modules 1316.The one or more processors 1304 may be configured through a combinationof software modules 1316 loaded during initialization, and furtherconfigured by loading or unloading one or more software modules 1316during operation.

In the illustrated example, the processing circuit 1302 may beimplemented with a bus architecture, represented generally by the bus1310. The bus 1310 may include any number of interconnecting buses andbridges depending on the specific application of the processing circuit1302 and the overall design constraints. The bus 1310 links togethervarious circuits including the one or more processors 1304, and storage1306. Storage 1306 may include memory devices and mass storage devices,and may be referred to herein as computer-readable media and/orprocessor-readable media. The storage 1306 may include transitorystorage media and/or non-transitory storage media.

The bus 1310 may also link various other circuits such as timingsources, timers, peripherals, voltage regulators, and power managementcircuits. A bus interface 1308 may provide an interface between the bus1310 and one or more transceivers 1312. In one example, a transceiver1312 may be provided to enable the apparatus 1300 to communicate with acharging or receiving device in accordance with a standards-definedprotocol. Depending upon the nature of the apparatus 1300, a userinterface 1318 (e.g., keypad, display, speaker, microphone, joystick)may also be provided, and may be communicatively coupled to the bus 1310directly or through the bus interface 1308.

A processor 1304 may be responsible for managing the bus 1310 and forgeneral processing that may include the execution of software stored ina computer-readable medium that may include the storage 1306. In thisrespect, the processing circuit 1302, including the processor 1304, maybe used to implement any of the methods, functions and techniquesdisclosed herein. The storage 1306 may be used for storing data that ismanipulated by the processor 1304 when executing software, and thesoftware may be configured to implement any one of the methods disclosedherein.

One or more processors 1304 in the processing circuit 1302 may executesoftware. Software shall be construed broadly to mean instructions,instruction sets, code, code segments, program code, programs,subprograms, software modules, applications, software applications,software packages, routines, subroutines, objects, executables, threadsof execution, procedures, functions, algorithms, etc., whether referredto as software, firmware, middleware, microcode, hardware descriptionlanguage, or otherwise. The software may reside in computer-readableform in the storage 1306 or in an external computer-readable medium. Theexternal computer-readable medium and/or storage 1306 may include anon-transitory computer-readable medium. A non-transitorycomputer-readable medium includes, by way of example, a magnetic storagedevice (e.g., hard disk, floppy disk, magnetic strip), an optical disk(e.g., a compact disc (CD) or a digital versatile disc (DVD)), a smartcard, a flash memory device (e.g., a “flash drive,” a card, a stick, ora key drive), RAM, ROM, a programmable read-only memory (PROM), anerasable PROM (EPROM) including EEPROM, a register, a removable disk,and any other suitable medium for storing software and/or instructionsthat may be accessed and read by a computer. The computer-readablemedium and/or storage 1306 may also include, by way of example, acarrier wave, a transmission line, and any other suitable medium fortransmitting software and/or instructions that may be accessed and readby a computer. Computer-readable medium and/or the storage 1306 mayreside in the processing circuit 1302, in the processor 1304, externalto the processing circuit 1302, or be distributed across multipleentities including the processing circuit 1302. The computer-readablemedium and/or storage 1306 may be embodied in a computer programproduct. By way of example, a computer program product may include acomputer-readable medium in packaging materials. Those skilled in theart will recognize how best to implement the described functionalitypresented throughout this disclosure depending on the particularapplication and the overall design constraints imposed on the overallsystem.

The storage 1306 may maintain and/or organize software in loadable codesegments, modules, applications, programs, etc., which may be referredto herein as software modules 1316. Each of the software modules 1316may include instructions and data that, when installed or loaded on theprocessing circuit 1302 and executed by the one or more processors 1304,contribute to a run-time image 1314 that controls the operation of theone or more processors 1304. When executed, certain instructions maycause the processing circuit 1302 to perform functions in accordancewith certain methods, algorithms and processes described herein.

Some of the software modules 1316 may be loaded during initialization ofthe processing circuit 1302, and these software modules 1316 mayconfigure the processing circuit 1302 to enable performance of thevarious functions disclosed herein. For example, some software modules1316 may configure internal devices and/or logic circuits 1322 of theprocessor 1304, and may manage access to external devices such as atransceiver 1312, the bus interface 1308, the user interface 1318,timers, mathematical coprocessors, and so on. The software modules 1316may include a control program and/or an operating system that interactswith interrupt handlers and device drivers, and that controls access tovarious resources provided by the processing circuit 1302. The resourcesmay include memory, processing time, access to a transceiver 1312, theuser interface 1318, and so on.

One or more processors 1304 of the processing circuit 1302 may bemultifunctional, whereby some of the software modules 1316 are loadedand configured to perform different functions or different instances ofthe same function. The one or more processors 1304 may additionally beadapted to manage background tasks initiated in response to inputs fromthe user interface 1318, the transceiver 1312, and device drivers, forexample. To support the performance of multiple functions, the one ormore processors 1304 may be configured to provide a multitaskingenvironment, whereby each of a plurality of functions is implemented asa set of tasks serviced by the one or more processors 1304 as needed ordesired. In one example, the multitasking environment may be implementedusing a timesharing program 1320 that passes control of a processor 1304between different tasks, whereby each task returns control of the one ormore processors 1304 to the timesharing program 1320 upon completion ofany outstanding operations and/or in response to an input such as aninterrupt. When a task has control of the one or more processors 1304,the processing circuit is effectively specialized for the purposesaddressed by the function associated with the controlling task. Thetimesharing program 1320 may include an operating system, a main loopthat transfers control on a round-robin basis, a function that allocatescontrol of the one or more processors 1304 in accordance with aprioritization of the functions, and/or an interrupt driven main loopthat responds to external events by providing control of the one or moreprocessors 1304 to a handling function.

In one implementation, the apparatus 1300 includes or operates as awireless charging device that has a battery charging power sourcecoupled to a charging circuit, a plurality of charging cells, one ormore driver circuits (see FIGS. 5 and 8 for example) and a controller,which may be included in one or more processors 1304. The one or moredriver circuits may be configured to decode ASK-modulated messages froma tank voltage or a current flowing in a transmitting coil. Theplurality of charging cells may be configured to provide a chargingsurface. At least one coil may be configured to direct anelectromagnetic field through a charge transfer area of each chargingcell. The one or more driver circuits may include a first driver circuitconfigured to drive a transmitting coil positioned near the surface ofthe charging device. The controller may be configured to cause thedriver circuit to provide a charging current to the transmitting coil,decode a request for lower transmission power from a modulation of thecharging current, reduce the amplitude of the charging current inaccordance with the request for lower transmission power when atemperature measured at a surface of the charging device is less than athreshold temperature, and initiate a cool down sequence when thetemperature measured at the surface of the charging device equals orexceeds the threshold temperature. In one example, the request for lowertransmission power may be provided in an ASK-modulated signalsuperimposed on the charging current.

In one example, one or more sensors may be thermoconductively coupled toa charging surface of the apparatus 1300 and configured to provideperiodic temperature measurements of at least a portion of the surfaceof the charging device. The threshold temperature level is obtained froma prior calibration performed during a charging procedure. Thetemperature measured at the surface of the charging device equaling orexceeding the threshold temperature may be indicative of a device beingcharged that has an internal temperature that exceeds a temperaturelimit.

In some examples, the threshold voltage level is maintained in a lookuptable. The lookup table may include a threshold temperature for each ofa plurality of device types. The controller may be further configured toprovide a minimum transmission power in response to the request forlower transmission power when initiating a cool down sequence. Thecontroller may be further configured to determine a gradient in a timeseries of temperature measurements measured at the surface of thecharging device, and terminate the charging current when the gradient inthe time series of temperature measurements indicates that the surfaceof the charging device will remain above a restart temperature definedfor a device being charged for a cool-down duration.

In some examples, the controller is further configured to determine agradient in a time series of temperature measurements measured at thesurface of the charging device, and may reduce power output of one ormore other driver circuits in the charging device when the gradient inthe time series of temperature measurements indicates that the surfaceof the charging device will remain above a restart temperature definedfor a device being charged for a cool-down duration.

In some examples, the controller is further configured to determine afirst gradient in a first time series of temperature measurementsmeasured at the surface of the charging device, terminate the chargingcurrent when the first gradient in the first time series of temperaturemeasurements indicates that the surface of the charging device willremain above a restart temperature defined for a device being chargedfor a first cool-down duration, determine a second gradient in a secondtime series of temperature measurements measured at the surface of thecharging device after terminating the charging current, and reduce poweroutput of one or more other driver circuits in the charging device whenthe second gradient in the second time series of temperaturemeasurements indicates that the surface of the charging device willremain above the restart temperature defined for the device beingcharged a second cool-down duration.

In certain examples, the storage 1306 maintains instructions andinformation where the instructions are configured to cause the one ormore processors 1304 to configure a driver circuit to drive atransmitting coil positioned near the surface of the charging device,cause the driver circuit to provide a charging current to thetransmitting coil, decode a request for lower transmission power from amodulation of the charging current, reduce the amplitude of the chargingcurrent in accordance with the request for lower transmission power whena temperature measured at a surface of the charging device is less thana threshold temperature, and initiate a cool down sequence when thetemperature measured at the surface of the charging device equals orexceeds the threshold temperature.

In some examples, the instructions may be configured to receive, obtainor retrieve temperature measurements from one or more sensors that arethermoconductively coupled to the surface of the charging device. Thevalue of the threshold temperature may be obtained from a priorcalibration performed during a charging procedure. The temperaturemeasured at the surface of the charging device equaling or exceeding thethreshold temperature may be indicative of a device being charged thathas an internal temperature that exceeds a temperature limit.

In some examples, the threshold voltage level is maintained in a lookuptable. The lookup table may include a threshold temperature for each ofa plurality of device types. The instructions may be configured toprovide a minimum transmission power in response to the request forlower transmission power when initiating the cool down sequence. Theinstructions may be configured to determine a gradient in a time seriesof temperature measurements measured at the surface of the chargingdevice, and terminate the charging current when the gradient in the timeseries of temperature measurements indicates that the surface of thecharging device will remain above a restart temperature defined for adevice being charged for a cool-down duration. The instructions may beconfigured to determine a gradient in a time series of temperaturemeasurements measured at the surface of the charging device, and reducepower output of one or more other driver circuits in the charging devicewhen the gradient in the time series of temperature measurementsindicates that the surface of the charging device will remain above arestart temperature defined for a device being charged for a cool-downduration.

In some examples, the instructions may be configured to determine afirst gradient in a first time series of temperature measurementsmeasured at the surface of the charging device, terminate the chargingcurrent when the first gradient in the first time series of temperaturemeasurements indicates that the surface of the charging device willremain above a restart temperature defined for a device being chargedfor a first cool-down duration, determine a second gradient in a secondtime series of temperature measurements measured at the surface of thecharging device after terminating the charging current, and reduce poweroutput of one or more other driver circuits in the charging device whenthe second gradient in the second time series of temperaturemeasurements indicates that the surface of the charging device willremain above the restart temperature defined for the device beingcharged a second cool-down duration.

FIG. 14 is a flowchart 1400 illustrating a method for operating acharging device in accordance with certain aspects of this disclosure.The method may be performed using a controller in the charging device.At block 1402, the controller may configure a driver circuit to drive atransmitting coil positioned near the surface of the charging device. Atblock 1404, the controller may cause the driver circuit to provide acharging current to the transmitting coil. At block 1406, the controllermay decode a request for lower transmission power from a modulation ofthe charging current. At block 1408, the controller may determinewhether an overtemperature condition exists or is indicated in a devicebeing charged. The overtemperature condition may correspond to atemperature of a battery exceeding a maximum temperature defined bystandards, protocol or designer. The overtemperature condition may beindicated when a temperature measured at the surface of the chargingdevice exceeds a threshold temperature. In one example, and at block1410, the controller may reduce the amplitude of the charging current inaccordance with the request for lower transmission power when atemperature measured at a surface of the charging device is less thanthe threshold temperature. In another example, and at block 1412, thecontroller may initiate a cool down sequence when the temperaturemeasured at the surface of the charging device equals or exceeds thethreshold temperature.

In some examples, the controller may receive temperature measurementsfrom one or more sensors that are thermoconductively coupled to thesurface of the charging device. A sensor may be thermoconductivelycoupled to the surface of the charging device when it is embedded in thesurface, or fixed or attached to the surface of the charging deviceusing a thermally conductive adhesive, for example. In some instances,the value of the threshold temperature may be obtained from a priorcalibration performed during a charging procedure. In some instances,the temperature measured at the surface of the charging device equalingor exceeding the threshold temperature is indicative of a device beingcharged that has an internal temperature that exceeds a temperaturelimit.

In certain examples, the threshold voltage level is maintained in alookup table. The lookup table may include a threshold voltage level foreach of a plurality of device types.

In certain examples, a cool down sequence may be initiated by providinga minimum transmission power in response to the request for lowertransmission power. A gradient in a time series of temperaturemeasurements measured at the surface of the charging device may bedetermined, estimated or calculated. The charging current may beterminated when the gradient in the time series of temperaturemeasurements indicates that the surface of the charging device willremain above a restart temperature defined for a device being chargedfor a cool-down duration. Power output of one or more other drivercircuits in the charging device may be reduced when the gradient in thetime series of temperature measurements indicates that the surface ofthe charging device will remain above a restart temperature defined fora device being charged for a cool-down duration.

In certain examples, a first gradient in a first time series oftemperature measurements measured at the surface of the charging devicemay be determined. The charging current may be terminated when the firstgradient in the first time series of temperature measurements indicatesthat the surface of the charging device will remain above a restarttemperature defined for a device being charged for a first cool-downduration. The first cool-down duration may be defined by standards,protocol or a system designer. A second gradient in a second time seriesof temperature measurements measured at the surface of the chargingdevice may be determined after terminating the charging current. Poweroutput of one or more other driver circuits in the charging device maybe reduced when the second gradient in the second time series oftemperature measurements indicates that the surface of the chargingdevice will remain above the restart temperature defined for the devicebeing charged a second cool-down duration.

The previous description is provided to enable any person skilled in theart to practice the various aspects described herein. Variousmodifications to these aspects will be readily apparent to those skilledin the art, and the generic principles defined herein may be applied toother aspects. Thus, the claims are not intended to be limited to theaspects shown herein, but is to be accorded the full scope consistentwith the language claims, wherein reference to an element in thesingular is not intended to mean “one and only one” unless specificallyso stated, but rather “one or more.” Unless specifically statedotherwise, the term “some” refers to one or more. All structural andfunctional equivalents to the elements of the various aspects describedthroughout this disclosure that are known or later come to be known tothose of ordinary skill in the art are expressly incorporated herein byreference and are intended to be encompassed by the claims. Moreover,nothing disclosed herein is intended to be dedicated to the publicregardless of whether such disclosure is explicitly recited in theclaims. No claim element is to be construed under the provisions of 35U.S.C. § 112, sixth paragraph, unless the element is expressly recitedusing the phrase “means for” or, in the case of a method claim, theelement is recited using the phrase “step for.”

What is claimed is:
 1. A method for operating a charging device,comprising: configuring a driver circuit to drive a transmitting coilpositioned near a surface of the charging device; causing the drivercircuit to provide a charging current to the transmitting coil; decodinga request for lower transmission power from a modulation of the chargingcurrent; reducing amplitude of the charging current in accordance withthe request for lower transmission power when a temperature measured ata surface of the charging device is less than a threshold temperature;and initiating a cool down sequence when the temperature measured at thesurface of the charging device equals or exceeds the thresholdtemperature.
 2. The method of claim 1, further comprising: receivingtemperature measurements from one or more sensors that arethermoconductively coupled to the surface of the charging device.
 3. Themethod of claim 1, wherein the threshold temperature is configured basedon a prior calibration performed during a charging procedure.
 4. Themethod of claim 1, wherein the temperature measured at the surface ofthe charging device equals or exceeds the threshold temperature isindicative of a device being charged that has an internal temperaturethat exceeds a temperature limit.
 5. The method of claim 1, wherein thethreshold temperature is defined in a lookup table.
 6. The method ofclaim 5, wherein the lookup table includes a threshold temperature foreach of a plurality of device types.
 7. The method of claim 1, whereininitiating a cool down sequence includes: providing a minimumtransmission power in response to the request for lower transmissionpower.
 8. The method of claim 7, further comprising: determining agradient in a time series of temperature measurements measured at thesurface of the charging device; and terminating the charging currentwhen the gradient in the time series of temperature measurementsindicates that the surface of the charging device will remain above arestart temperature defined for a device being charged for a cool-downduration.
 9. The method of claim 7, further comprising: determining agradient in a time series of temperature measurements measured at thesurface of the charging device; and reducing power output of one or moreother driver circuits in the charging device when the gradient in thetime series of temperature measurements indicates that the surface ofthe charging device will remain above a restart temperature defined fora device being charged for a cool-down duration.
 10. The method of claim7, further comprising: determining a first gradient in a first timeseries of temperature measurements measured at the surface of thecharging device; terminating the charging current when the firstgradient in the first time series of temperature measurements indicatesthat the surface of the charging device will remain above a restarttemperature defined for a device being charged for a first cool-downduration; determining a second gradient in a second time series oftemperature measurements measured at the surface of the charging deviceafter terminating the charging current; and reducing power output of oneor more other driver circuits in the charging device when the secondgradient in the second time series of temperature measurements indicatesthat the surface of the charging device will remain above the restarttemperature defined for the device being charged a second cool-downduration.
 11. A charging device, comprising: a driver circuit configuredto drive a transmitting coil positioned near a surface of the chargingdevice; and a controller configured to: cause the driver circuit toprovide a charging current to the transmitting coil; decode a requestfor lower transmission power from a modulation of the charging current;reduce amplitude of the charging current in accordance with the requestfor lower transmission power when a temperature measured at a surface ofthe charging device is less than a threshold temperature; and initiate acool down sequence when the temperature measured at the surface of thecharging device equals or exceeds the threshold temperature.
 12. Thecharging device of claim 11, further comprising: one or more sensorsthermoconductively coupled to the surface of the charging device andconfigured to provide periodic temperature measurements of at least aportion of the surface of the charging device.
 13. The charging deviceof claim 11, wherein the threshold temperature is configured based on aprior calibration performed during a charging procedure.
 14. Thecharging device of claim 11, wherein the temperature measured at thesurface of the charging device equals or exceeds the thresholdtemperature is indicative of a device being charged that has an internaltemperature that exceeds a temperature limit.
 15. The charging device ofclaim 11, wherein the threshold temperature is defined in a lookuptable.
 16. The charging device of claim 15, wherein the lookup tableincludes a threshold temperature for each of a plurality of devicetypes.
 17. The charging device of claim 11, wherein the controller isfurther configured to: provide a minimum transmission power in responseto the request for lower transmission power when initiating a cool downsequence.
 18. The charging device of claim 17, wherein the controller isfurther configured to: determine a gradient in a time series oftemperature measurements measured at the surface of the charging device;and terminate the charging current when the gradient in the time seriesof temperature measurements indicates that the surface of the chargingdevice will remain above a restart temperature defined for a devicebeing charged for a cool-down duration.
 19. The charging device of claim17, wherein the controller is further configured to: determine agradient in a time series of temperature measurements measured at thesurface of the charging device; and reduce power output of one or moreother driver circuits in the charging device when the gradient in thetime series of temperature measurements indicates that the surface ofthe charging device will remain above a restart temperature defined fora device being charged for a cool-down duration.
 20. The charging deviceof claim 17, wherein the controller is further configured to: determinea first gradient in a first time series of temperature measurementsmeasured at the surface of the charging device; terminate the chargingcurrent when the first gradient in the first time series of temperaturemeasurements indicates that the surface of the charging device willremain above a restart temperature defined for a device being chargedfor a first cool-down duration; determine a second gradient in a secondtime series of temperature measurements measured at the surface of thecharging device after terminating the charging current; and reduce poweroutput of one or more other driver circuits in the charging device whenthe second gradient in the second time series of temperaturemeasurements indicates that the surface of the charging device willremain above the restart temperature defined for the device beingcharged a second cool-down duration.